The problem of exhaustion of valuable metal mineral resources that has been recently issued is expected to be an obstacle to development of human civilization in near future.
For example, strontium is a resource that has been generally used throughout the chemical and ceramic industry, but Korea has no mine and depends on imports for the whole quantity of strontium. Further, the amount of strontium deposits estimated around the world is not much, so the reserves-to-production ratio of strontium is expected as 10 to 30 years, even considering price rises, so the possibility of exhaustion of strontium is estimated as being very high.
However, the content of strontium in the seawater has been found as about 8 mg/L and the strontium deposits in the seawater has been found as being almost infinite, considering the content and the total amount of the seawater. Accordingly, many countries, including Korea, have made great efforts to develop a technique for extracting strontium from the seawater, and recently, some of the techniques have achieved the expected results for extracting strontium.
Further, lithium that is a mineral resource is the raw material of not only various IT products or electronic products such as a mobile phone, a notebook, and a camcorder, which occupy a large portion of the economic development of Korea, but the secondary battery necessary for hybrid electric vehicles, and is also national strategic metal used for special alloys for aircrafts and the fuel for nuclear fusion power generation.
Considering the economical efficiency of lithium that is a mineral resource, the amount of lithium mined from the ground around the world is at most about 4,100,100 tons and lithium is a rare resource expected to be exhausted within ten years later.
In order to recover lithium from the nature in the related art, there are a method of recovering it from minerals through roasting or exudation using sulfuric acid, a method of recovering it from naturally vaporizing salt lakes, and a method of extracting it from the seawater.
However, the lithium resource is limited in some countries and it is practically impossible to apply the method of obtaining lithium from minerals and salt lakes to Korea having little lithium deposits. However, it has been known that the content of lithium in dissolved resources in the seawater is very small as 0.17 mg/l, but the entire dissolved amount is very large as 2,300 hundred million tons.
As described above, a great amount of dissolved resources necessary for keeping the modern human life are contained in the seawater. Accordingly, a technology of recovering minerals that can selectively extract specific valuable metal ions dissolved in the seawater reduces the degree of dependency on foreign country resources and allows for stable supply of resources, so it has a sufficient value as an economic growth driver of Korea and is a very important technology for keeping developing the economy in the future.
Most techniques related to recovery of valuable metal from the seawater in the related art have been developed with a focus on exchange and adsorption of ions of inorganic or organic substances for selectively removing specific metal ions.
However, the techniques of recovering ions from the seawater in the related art was designed to recover only a specific kind of ion in the seawater and can recover only a specific kind of ion from mother liquor such as the seawater containing various kinds of ions, so it is not efficient, and a plurality of specific systems for recovering each of ions are specifically required to separately adsorb and recover various ions using the conventional system, so it is not economical.
Further, according to the techniques of recovering ions in the related art, a plurality of apparatuses is arranged in series to increase the efficiency of recovering single specific ion. Therefore, according to these techniques of recovering ions having this configuration in the related art, deionized water (cleansing water) supplied to remove non-adsorbed ions is discharged, so when the amount of the deionized water is insufficient, the deionized water to be supplied for the process of recovering the desired ions is not sufficiently supplied, so the recovery efficiency is reduced. Further, when ions are recovered from cells that have undergone the adsorption process, the whole systems connected in series should be stopped, so the efficiency of operation is also largely decreased.